proc_lib

Functions for asynchronous and synchronous start of processes adhering to the OTP design principles.

This module is used to start processes adhering to
the OTP Design Principles. Specifically, the functions in this
module are used by the OTP standard behaviors (gen_server,
gen_fsm, ...) when starting new processes. The functions
can also be used to start special processes, user
defined processes which comply to the OTP design principles. See
Sys and Proc_Lib in OTP Design Principles for an example.

Some useful information is initialized when a process starts.
The registered names, or the process identifiers, of the parent
process, and the parent ancestors, are stored together with
information about the function initially called in the process.

While in "plain Erlang" a process is said to terminate normally
only for the exit reason normal, a process started
using proc_lib is also said to terminate normally if it
exits with reason shutdown or {shutdown,Term}.
shutdown is the reason used when
an application (supervision tree) is stopped.

When a process started using proc_lib terminates
abnormally -- that is, with another exit reason than normal,
shutdown, or {shutdown,Term} -- a crash report
is generated, which is written to terminal by the default SASL
event handler. That is, the crash report is normally only visible
if the SASL application is started. See
sasl(6) and
SASL User's Guide.

The crash report contains the previously stored information such
as ancestors and initial function, the termination reason, and
information regarding other processes which terminate as a result
of this process terminating.

start_link(Module, Function, Args, Time, SpawnOpts) -> Ret

Starts a new process synchronously. Spawns the process and
waits for it to start. When the process has started, it
must call
init_ack(Parent,Ret)
or init_ack(Ret),
where Parent is the process that evaluates this
function. At this time, Ret is returned.

If the start_link/3,4,5 function is used and
the process crashes before it has called init_ack/1,2,
{error, Reason} is returned if the calling process
traps exits.

If Time is specified as an integer, this function
waits for Time milliseconds for the new process to call
init_ack, or {error, timeout} is returned, and
the process is killed.

The SpawnOpts argument, if given, will be passed
as the last argument to the spawn_opt/2,3,4,5 BIF.

Note!

Using the spawn option monitor is currently not
allowed, but will cause the function to fail with reason
badarg.

init_ack(Ret) -> ok

Ret = term()

init_ack(Parent, Ret) -> ok

Parent = pid()

Ret = term()

This function must used by a process that has been started by
a start[_link]/3,4,5
function. It tells Parent that the process has
initialized itself, has started, or has failed to initialize
itself.

format(CrashReport) -> string()

CrashReport = [term()]

Equivalent to format(CrashReport, latin1).

format(CrashReport, Encoding) -> string()

CrashReport = [term()]

Encoding = latin1 | unicode | utf8

This function can be used by a user defined event handler to
format a crash report. The crash report is sent using
error_logger:error_report(crash_report, CrashReport).
That is, the event to be handled is of the format
{error_report, GL, {Pid, crash_report, CrashReport}}
where GL is the group leader pid of the process
Pid which sent the crash report.

initial_call(Process) -> {Module, Function, Args} | false

Extracts the initial call of a process that was started
using one of the spawn or start functions described above.
Process can either be a pid, an integer tuple (from
which a pid can be created), or the process information of a
process Pid fetched through an
erlang:process_info(Pid) function call.

Note!

The list Args no longer contains the actual arguments,
but the same number of atoms as the number of arguments; the first atom
is always 'Argument__1', the second 'Argument__2', and
so on. The reason is that the argument list could waste a significant
amount of memory, and if the argument list contained funs, it could
be impossible to upgrade the code for the module.

If the process was spawned using a fun, initial_call/1 no
longer returns the actual fun, but the module, function for the local
function implementing the fun, and the arity, for instance
{some_module,-work/3-fun-0-,0} (meaning that the fun was
created in the function some_module:work/3).
The reason is that keeping the fun would prevent code upgrade for the
module, and that a significant amount of memory could be wasted.

translate_initial_call(Process) -> {Module, Function, Arity}

This function is used by the c:i/0 and
c:regs/0 functions in order to present process
information.

Extracts the initial call of a process that was started
using one of the spawn or start functions described above,
and translates it to more useful information. Process
can either be a pid, an integer tuple (from which a pid can
be created), or the process information of a process
Pid fetched through an erlang:process_info(Pid)
function call.

If the initial call is to one of the system defined behaviors
such as gen_server or gen_event, it is
translated to more useful information. If a gen_server
is spawned, the returned Module is the name of
the callback module and Function is init
(the function that initiates the new server).

A supervisor and a supervisor_bridge are also
gen_server processes. In order to return information
that this process is a supervisor and the name of the
call-back module, Module is supervisor and
Function is the name of the supervisor callback
module. Arity is 1 since the init/1
function is called initially in the callback module.

By default, {proc_lib,init_p,5} is returned if no
information about the initial call can be found. It is
assumed that the caller knows that the process has been
spawned with the proc_lib module.

hibernate(Module, Function, Args) -> no_return()

Module = module()

Function = atom()

Args = [term()]

This function does the same as (and does call) the BIF
hibernate/3,
but ensures that exception handling and logging continues to
work as expected when the process wakes up. Always use this
function instead of the BIF for processes started using
proc_lib functions.